Activity and proximity patterns of 25 free-ranging juvenile howling monkeys in 5 social groups in Guanacaste Province were compared for age and sex differences. Observations were based on 709.5 hours of focal observations from June-August, 1993-1996. Twelve males and 13 females between the ages of 0.8 and 3.8 years of age were focal subjects. Duration data (rest, feed, travel, play) and proximity to mother (contact, less than 1 meter, less than 5 meters) were converted to mean minutes per hour, and duration data for proximity to adult males, adult females and juveniles were also adjusted for number of interactors available. Comparisons were made for age and sex using ANOVA. There were no significant differences by age or by sex in activity patterns or proximity to other group members. There were no significant sex differences in proximity to mother, but there was a significant difference by age. As they got older, both males and females increased the amount of time spent out of contact or out of proximity (>5m) to mother, but no differences in the other proximity patterns, indicating that juveniles stay near mothers. This lack of overall difference between males and females at the juvenile stage is remarkable since differences in male and female infant behavior are well documented. There do not appear to be sex-specific behavioral patterns for juvenile howling monkeys, paralleling their physical monomorphism at this same developmental period.